Vehicles of the type driven by a motor such as an electric car, a hybrid vehicle, a fuel cell vehicle and the like have a power supply unit including secondary batteries of relatively high capacity (battery pack) mounted. Such a battery pack obtains high voltage by the series connection of a plurality of batteries such as a lead storage battery, nickel metal hydride battery, lithium-ion battery, and the like.
An assembly type secondary battery (battery module) is generally employed for a battery pack. A battery module is configured having a plurality of (for example, 6) electric cells (for example, a battery cell having an output voltage of 1.2V) linked integrally so as to obtain the required power capacity (voltage value). A predetermined number of such battery modules are connected in series to constitute a battery pack that can provide a high voltage output of 200V to 300V.
In the battery pack, the plurality of battery modules of rectangular parallelepiped shape have their sides of larger width facing each other to be arranged in a stacked configuration. An end plate is abutted against the outer side of the cell of the battery modules located at either end. These end plates are bound by a restrain band to be connected together.
The configuration of a battery cell (for example, a nickel metal hydride battery) in a battery pack will be described hereinafter. Layers of a cathode plate and an anode plate are stacked with a separator therebetween to form a group of plates identified as a power generator element. The group of plates is accommodated in a cell together with an electrolyte. The opening of each cell is closed by a lid equipped with a safety valve. A lead is pulled out upwards from the upper end side of each cathode plate constituting the group of plates to be connected to a positive terminal. Similarly, a lead is pulled out upwards from the upper end of the other side of each anode plate to be connected to a negative terminal. These positive and negative terminals are attached to the lid.
In a battery pack, heat is generated by the chemical reaction occurring within the battery cell. This generated heat will induce deficiency such as reduction in the battery capacity and battery lifetime if the generated heat is neglected. In the case where battery modules are incorporated in a vehicle, a gap corresponding to a channel of air identified as a cooling medium is provided to deliver or draw in air from the interior or exterior of the vehicle, whereby the battery pack is cooled down.
Japanese Patent Laying-Open No. 2004-47426 discloses a cooling apparatus for a battery module cooling each secondary battery efficiently and uniformly while suppressing the height of the battery module and the cooling apparatus. This battery module cooling apparatus includes a cooling medium channel formed to pass a cooling medium in a lateral direction orthogonal to the vertical direction between each of the plurality of second batteries arranged in parallel in a battery module, and cooling medium feeding means for feeding a cooling medium towards the cooling medium channel. The cooling medium feeding means includes a pair of cooling medium introduction ducts at both the left and right sides of the battery module, having the outlet formed so as to feed the cooling medium alternately in opposite lateral directions with respect to each cooling medium channel, and cooling medium pressure feeding means for supplying the cooling medium to the two cooling medium introduction ducts.
In this battery module cooling apparatus, the cooling medium channel through which a cooling medium flows in the lateral direction is formed between the side faces of adjacent cuboid secondary batteries with a rectangular side face having a height larger than the thickness dimension and a lateral width larger than the height dimension. The cooling medium feeding means is provided to deliver the cooling medium towards the cooling medium channel. By the flow of a cooling medium to the cooling medium channel between respective rectangular side faces of the secondary batteries from the left and right directions of the battery module, each secondary battery of small thickness can be cooled effectively. Further, the height of the battery module including the cooling apparatus can be suppressed since cooling medium feeding means does not have to be provided above and below the battery module. This is advantageous from the standpoint of ensuring the space for mounting the battery module identified as the vehicle driving power supply.
Although the dimension in the direction of height of the secondary batteries can be suppressed in the battery module with the cooling apparatus disclosed in Japanese Patent Laying-Open No. 2004-47426, the following problems are noted. It is assumed that such formed secondary batteries are mounted on a vehicle with the arranged direction of the secondary batteries corresponding to the direction of width (transversing direction) of the vehicle (most usage applications correspond to this mounting direction). Although the mountability of the battery module above the floor panel and beneath the seat is favorable since the dimension in the direction of height is suppressed, the cooling medium channel disposed in the longitudinal direction of the vehicle, i.e. lengthways from the front to the back or from the back to the front of the vehicle, will have increased dimension in that direction. This means that, when the battery module is mounted beneath the front seat, the space in the neighborhood of the toes of the rider on the rear seat may become smaller. In the case where the battery module is mounted in the proximity of the rear wheel of a vehicle having two rows of seats, it may become an obstacle in taking out the spare tire stored in the recess provided at the floor panel.
Such a problem is not limited to a secondary battery, and is encountered common to secondary batteries (rechargeable batteries), capacitors, fuel cells, PCUs, and the like that require cooling by air or air circulation.